Implantable Cardioverter Defibrillators (ICD's) have decreased substantially in volume in recent years, but are still larger than desirable. The high energy discharge capacitors that create the defibrillation pulse are typically the largest components in the device, normally at about 12 cubic centimeters for a 30 Joule device. In addition to small size, it is desirable for the ICD to have a curved profile for patient comfort. As the curved ICD shrinks in size, it becomes more and more necessary for internal components to also be curved to achieve a volume-efficient design.
Defibrillators with aluminum electrolytic capacitors that have a curved profile are currently in use. These capacitors have a “D”-shape which generally fits into the curved bottom or side of the defibrillator can. However, these capacitors are still larger than desirable, and are not likely to reach more than about 4-5 Joules per cubic centimeter in volumetric energy density. “D”-shaped tantalum capacitors for ICD's have also been reported. These capacitors are slightly higher in volumetric energy density than aluminum electrolytic capacitors, but they are much heavier. The weight of these are about 6 grams per cubic centimeter in a finished capacitor.
Another class of capacitors include those generally referred to as ceramic capacitors. Although within that general class there are different constructions, one of these includes the lead lanthanum zirconium titanate (PLZT) ceramic construction. PLZT ceramic capacitors may be useful as high energy discharge capacitors for implantable cardioverter defibrillators. These capacitors are capable of energy densities as high as about 7 Joules per cubic centimeter, compared to about 2.5 to 3 Joules per cubic centimeter that is currently available.